In my quest to devour as many teaching books as possible over winter break, I've been reading the fantastic book Number Sense Routines: Building Numerical Literacy Every Day in Grades K-3 by Jessica Shumway. It's filled with ideas on how to incorporate routines that build number sense every day. My district uses the Everyday Mathematics curriculum, which touches on a lot of the teaching practices that help grow number sense. But it doesn't seem to have an orderly, progressive and easily understandable description of how number sense develops as children's brains grow. How do I know when kids are ready to start decomposing numbers? If a kindergartener can count to 50 but can't do one-to-one correspondence [pointing to one item at a time while they count up], is he ready to start decomposing teen numbers? Will a kindergartener be able to point out which amount is more and which is less, if she can't count?
Fortunately, the Number Sense Routines book explains all this! They include a wonderful description of the number sense learning trajectory, which I decided to write up in a cute flow chart. I printed out the chart and have it in my lesson plan book. I use this to plan what's next for each of my math groups, based on where they are on this flow chart. For example, if they are still working on one-to-one correspondence, I know they aren't yet ready to tackle composing and decomposing numbers.

Click here or the picture above to download the chart. Hope it helps you too!